1. Field
One aspect of this invention relates to humic acid-containing materials having an enhanced electronegative surface charge. Another aspect of this invention relates to the use of humic acid-containing materials having an enhanced surface charge to decrease the viscosity of aqueous, clay-containing drilling fluids.
2. Prior Art
Humus, organic matter which is more or less decomposed anerobically, is formed on the floors of forests from decomposed leaves and other detritus, in soils, on the bottom of ponds and lakes from organic matter grown or deposited therein; it occurs in peat bags, in lignite and brown coal deposits and many other types of minerals and soils, such as Leonardite, Aguja, and titanium mineral deposits. When any of these materials is treated with alkali, an organic fraction called humic substance dissolves. If the resulting solution is acidified to pH 2 to 3, some of the organic matter precipitates; this material is called humic acid, and the portion which remains in solution are called fulvic acid and ulmic acid. The exact structures of humic acids are unknown, and they are extremely variable. The principal organic groups present are phenolic and carboxylic OH, aliphatic CH, carbonyl, conjugated carbonyl or aromatic CH.sub.2 or CH.sub.3 or ionic carboxyl, and possible others. The average molecular weight of the humic acids is between 5,000 and 50,000. They have no X-ray or electron diffraction patterns and are therefore presumable amorphous. Humic acids have a large cation exchange capacity which varies from about 200 to about 500 milliequivalents per 100 grams at pH 7 depending on the humus source. Humic acids are colloids. When the cation exchange sites on the humic molecule are filled predominantly with other than hydrogen, the material is called humate. The humates of monovalent inorganic and ammonium ions are soluble or colloidally dispersable in water, but the humates of multivalent cations are insoluble.
Humic acid is also obtained by the controlled oxidation of coal. See for example Schulz et al. U.S. Pat. No. 4,305,728, column 2, lines 6-51, incorporated herein be reference.
The use of humic acid-containing materials and humates in aqueous base, clay-containing drilling fluids or "muds" to decrease the viscosity and gel strength or decrease the fluid loss is well known, as exemplified by the following U.S. Pat. Nos.: Lawton et al. 1,999,766; Wayne 2,334,051; Rahn 2,650,197; Wilson 2,782,163; Chisholm 3,009,874; Stuchell et al. 3,027,322; Firth 4,311,600. Also various derivatives of humic acid or humic acid-containing materials have also been disclosed for this use in drilling fluids as exemplified by the following U.S. Pat. Nos.: Crowley et al. 2,813,826 and 2,813,827; Monroe 3,034,982 and 3,039,958; Moschopedis 3,352,902 and 3,700,728.
Humic acid may be extracted from humic acid-containing materials in a relatively pure, concentrated form for further use. Representative U.S. patents which disclose various processes for extracting humic acid from its source material are: Burdick U.S. Pat. No. 2,992,093; Karchet U.S. Pat. Nos. 3,111,404 and 3,544,296; Schwartz et al. U.S. Pat. No. 3,398,186; Chambers et al. U.S. Pat. No. 3,770,411; Goff U.S. Pat. No. 4,319,041; Moran et al. U.S. Pat. No. 4,459,149.
Funk U.S. Pat. No. 4,416,666 discloses aqueous deashed coal slurries containing a high concentration of coal and having a low viscosity wherein the colloidal sized coal particles have a zeta potential from about 15.4 to about 70.2 millivolts, preferably a negative surface charge from about -15.4 to about -70.2 millivolts. The surface charge is obtained by the addition of dispersing agents ot the coal slurry, preferably anionic dispersants.